netdev - Re: [PATCH net-next v4 2/3] virtio_net: add optional flow dissection in virtio_net_hdr_to

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Date:   Wed, 9 Jun 2021 21:05:33 -0700
From:   Alexei Starovoitov <alexei.starovoitov@...il.com>
To:     Jason Wang <jasowang@...hat.com>
Cc:     Willem de Bruijn <willemdebruijn.kernel@...il.com>,
        Tanner Love <tannerlove.kernel@...il.com>,
        Network Development <netdev@...r.kernel.org>,
        David Miller <davem@...emloft.net>,
        Alexei Starovoitov <ast@...nel.org>,
        Daniel Borkmann <daniel@...earbox.net>,
        Andrii Nakryiko <andrii@...nel.org>,
        Eric Dumazet <edumazet@...gle.com>,
        Petar Penkov <ppenkov@...gle.com>,
        Jakub Kicinski <kuba@...nel.org>,
        "Michael S . Tsirkin" <mst@...hat.com>,
        Tanner Love <tannerlove@...gle.com>
Subject: Re: [PATCH net-next v4 2/3] virtio_net: add optional flow dissection
 in virtio_net_hdr_to_skb

On Wed, Jun 9, 2021 at 8:53 PM Jason Wang <jasowang@...hat.com> wrote:
>
>
> It works but it couples virtio with bpf.

Jason,

I think your main concern is that it makes virtio_net_hdr into uapi?
That's not the case. __sk_buff is uapi, but pointers to sockets
and other kernel data structures are not.
Yes. It's a bit weird that uapi struct has a pointer to kernel internal,
but I don't see it as a deal breaker.
Tracing progs have plenty of such cases.
In networking there is tcp-bpf where everything is kernel internal and non-uapi.
So after this patch virtio_net_hdr is free to change without worrying about bpf
progs reading it.